Overhead projectors are often used for making presentations of printed matter, sketches, charts, and the like, such as those presentations made by salesmen, executives, or teachers. Clear sheets (transparencies) are prepared with images of the matter to be presented and then the transparencies are positioned on a transparency platform of the overhead projector during the presentation. The overhead projector then projects the image of the transparency onto a screen, wall or other, preferably flat, projection surface.
Many overhead transparency presentations are plagued with the following problems: as each transparency is replaced on the transparency platform, proper orientation must be established for each transparency requiring the presenter to determine if the audience can see each image and requiring the transparency to be moved "up and down" and from "side-to-side" until it is properly oriented; the transparencies are often smaller than the overhead projector's light area, causing transparencies to be surrounded by unwanted bright light; if a transparency is touched during the presentation, they will often move on the transparency platform and require readjustment; as transparencies are changed during a presentation, a blank projector screen can become annoying and detract from a presentation; transparencies that are constantly reused can get smudged and soiled, detracting from the presentation; a presenter may need to write or otherwise mark a slide during a presentation which causes the slide to be spoiled or stained; transparencies are often stored or filed in a folder after a presentation, causing the transparencies to become bent and difficult to use for other presentations; and a "pile of transparencies" is difficult to work with while standing at the projector, and individual transparencies are difficult to locate during a presentation. Using a loose sheet of covering paper to progressively reveal the transparency is impractical because the covering paper will often move from or fall off the presentation platform. Further, some methods of covering all or part of the transparency allow "ghosting" such that a faint version of the image is projected. Finally, a presenter often wants to reveal only a part of a transparency.
The transparency presentation device described in U.S. Pat. No. 4,688,910 to Deary attempts to solve the problems associated with overhead transparency presentations. The Deary device includes a support frame having an aperture or view window through which light is projected. The support frame is secured to the presentation platform of an overhead projector and a box-like aperture cover having a top, bottom, and sidewalls encloses the support frame. The aperture cover may be moved from an open to a closed position alternately exposing and concealing the aperture. A transparency is preferably placed so that it extends across the aperture and lays above the top of the aperture cover. Although the Deary device solves some of the problems relating to overhead transparency presentations mentioned above, several problems persist. For example, since the transparency lies above the aperture cover, with overhead projectors having a light source incorporated in the lens assembly, the image on the transparency is "ghosted" onto the projection surface so that an audience is able to see the image faintly when the aperture cover is in the closed position. Another problem is caused by the thickness of the support frame and aperture cover. The thickness causes the image on transparency to be distorted or partially distorted along the edge of the aperture cover thus making it difficult to read and difficult to mark the transparency. Yet another problem is that the aperture cover of the Deary device only allows the gradual revealing of a transparency in one direction. The present invention prevents "ghosting", allows the transparency to lay flat on the transparency platform, and may allow gradual revealing of the transparency in multiple directions.
Accordingly, an object of the present invention is to provide a reusable presentation frame for overhead transparencies that establishes a single orientation and position for each presentation frame so that multiple overhead transparencies may be placed and replaced without need for reorientation. Another object of the present invention is to provide a means for eliminating unwanted bright light when a transparency is smaller than the light area of the overhead projector. A further object of the present invention is to prevent transparencies that are constantly reused from getting smudged and soiled and thus detracting from the presentation. Yet another object of the present invention is to provide a means for easy storage or filing in binders when the transparencies are not in use. Further, an object of the present invention is to provide a means for preventing the "ghosting" of an image. Finally, an additional object of the present invention is to allow a range of concealment of overhead transparencies as they are projected by an overhead projector.